Oxidation of hydroxyl-containing aliphatic compounds



nite States OXIDATION on 'noxrL-coNrAc nrnnnrrc coMronNns No Drawing. Application July 31, 1%3, Serial NO. 371,'711

14 Claims. '(Cl. v26ll- 488) This invention pertains -to the oxidation of hydroxylcontaining aliphatic compounds by means of tetravalent leadcompounds. The reaction involves a cleavage of the carbon chains of the aliphatic compounds.

It has been-known in the priorart that lead tetraacetate causes cleavage of aliphatic compounds containing two adjacent hydroxyl groups with the formation of aldehydes. This reaction has been used'to qualitatively analyze for this type of grouping. Another reaction of lead tetraacetatehas been known, namely, the acetoxylation of :an active methylene group.

It is an object of this invention to use tetravalent lead compounds in the cleavage of hydroxy aliphatic compounds which do not contain hydroxyl groups on adjacent carbon atoms. Other objects will be apparent from the following description of the invention.

It has now been found that tetravalent lead compounds can be used in the cleavage of hydroxy aliphatic compounds having a particular configuration. Thus, this reaction can be applied to compounds characterized by the formula wherein R is selected from the group consisting of H, COOH, and alkyl groups, R is selected from the group consisting of H andalkyl groups, R is selected from the group consisting of H, alkyl, OH, and M groups, wherein M is an alkali metal, R is selected from the group consisting of H and monovalent aliphatic groups, the latter being made up of atoms selected from the group consisting of C, H, and O atoms, and R is selected from the group consisting of O and di-valent aliphatic groups, the latter being made up of atoms selected from the group consisting of C, H, and O atoms, together with, when R contains a COOH group, the salts and amides thereof. Typical aliphatic compounds which are subject to cleavage according to the process of this invention include compounds such as allyl carbinol, beta-hydroxypropionaldehyde, hy-

dracrylic acid, citric acid and the alkali metal salts thereof, malic acid, citramalic acid, agaracinic acid, norcaperatic acid, beta-hydroxybutyr-ic acid, beta hydroxyvaleric acid, beta-hydroxyisovaleric acid, beta-acetylethyl alcohol, 2,5-hexanedion-3-ol, diacetone alcohol, methylacetonyl carbinol, and aldol condensation products as exemplified by acetaldol and heptaldol, as well as ricinoeyl derivatives, such as methyl ricinoleate, butyl ricinoleate, castor oil, ricinoleic acid, ricinolleyl alcohol, ricinoleic acid salts, and ricinoleic amides.

The tetravalent lead compounds, suitable for use in effecting the oxidative cleavage reactions, are tetravalent lead salts of aliphatic carboxylic acids having from 2 to 6 carbon atoms per molecule, such as acetic acid, propionic acid, pivalic acid, and caproic acid. Tetravalent lead compounds which yield salts with these acids are also satisfactory for use in the process of this invention. Such compounds include red lead and lead dioxide. It is deatcnt phase separation,

sirable to use "the tetravalent lead compound in slight stoichiometric' excess.

Thecleavage reaction is carried out in the presence of a suitable solvent, such as one of the aforesaid aliphatic carboxylicacids having from 2 to 6 carbon atoms per molecule. This acid should be present in suificient amount to dissolve the aliphatic compound being oxidized. Also, when the tetravalent lead salt is being formed in situ, sufficient additional aliphatic acid should be present to react with the lead compound charged to the reactor. Other suitable reaction media include aromatic hydrocarbons, nitro-aromatic hydrocarbons, and chlorinated aliphatic hydrocarbon, typical examples of such solvents being benzene, nitro-benzene, chloroform, carbon tetrachloride, and di-chloroethylene.

The cleavage reaction proceeds at temperatures ranging from about 10to-.about 200 C. The maximum reaction temperature will be governed by the boiling point ofthe solvent, as it is preferable to conduct the reaction below such boiling point. The preferred reaction temperature is in the range from about 35 C. to about 45 C. Since the cleavage reaction is exothermic, cooling of thereaction mixture is required in order to maintain the preferred reaction temperature. A measure of the completion of the reaction is given by the point beyond which cooling-ofthereaction mixture is not required to maintain the temperaturein the preferred range.

The recovery of the reaction products is preferably effected, in the case of ricinoleyl compounds,'by mixing the reaction mixture with a large volume of water to cause a separating the upper phase, washing that phase free from aliphatic acid and lead compounds, and distilling the washed phase to. recover a distillate and an acyloxy aliphatic compound as'a residue. Steam distillation orspargingwith carbon dioxide are desirable methods of effecting the indicated distillation step. The distillate and residue may be dried by methods known to the art, such as by drying them over anhydrous sodium sulfate. The purity of the dried fractions can be improved by subjecting them to vacuum distillation. Modifications of this technique can be used in recovering the cleavage products formed from non-ricinoleyl starting materials.

The process of this invention appears to involve a cleavage reaction, the cleavage taking place at the bond joining the carbon atoms to which the R and R groups are attached, as per the above general formula for the grouping which is characteristic of the starting materials for this invention. The cleavage product containing the R group is an aldehyde when R is hydrogen, and otherwise is a keto derivative. The other cleavage product, to which the R groupis attached, is characterizedby having an acyloxy group (from the tetravalent lead compound) attached to the carbon atom bearing the R group. The process of this invention can serve as a means of preparing, either directly or through modification of the cleavage reaction products, a series of aldehydes, ketones, saturated and unsaturated hydroxy acids, diols, dibasic acids, and their corresponding acyloxy and alkyl and aryl esters.

As indicated above, it has been known that cleavage could be eflected in the case of compounds containing adjacent hydroxyl groups. It has also been known that compounds such as lead tetraacetate will acetoxylate nonhydroxy compounds containing active methylene groups, but, in the case of such compounds, no cleavage occurs. According to the present invention, it has been found that cleavage occurs in compounds containing one hydroxyl group, which is attached to a carbon atom which is adjacent to a carbon atom bearing an active hydrogen atom; additionalhydroxy groups may be present, provided that no hydroxyl group is attached to the carbon atom bearing the active hydrogen atom. If there is no hydroxyl group in the molecule, acyloxylation is the only reaction which occurs. Further, if the starting material is an acyloxy compound, rather than a hydroxy compound, no cleavage occurs. The unexpected nature of the process of this invention is thus readily evident, since it has not been previously known that compounds not containing adjacent hydroxyl groups would cleave or that such compounds containing active methylene groups would cleave. 1

Examples of the novel process of this invention are presented below:

Example 1.-Preparati0n of lead tetraacetate 5530 parts by weight of glacial acetic acid and 3920 parts by weight of acetic anhydride were added to a glass flask which was partially submerged in a steam bath.

When the temperature of the flask contents had reached Example 2.0xidation of sodium citrate A solution of sodium citrate in acetic acid was prepared. Lead tetraacetate cake was added in portions to this solution. stoichiometric excess, so as to ensure the complete reaction of the lead tetraacetate. Upon the addition of the lead tetraacetate, an exothermic reaction took place with the formation of a yellow precipitate. The latter was separated by filtration, washed with water to remove unreacted sodium citrate and acetic acid, and dried. The

product is a mixture of the salts of oxaloacetic acid and acetoxyglycolic acid.

Example 3.-0xidation. of diacetone alcohol A solution of diacetone alcohol in acetic acid was prepared, and to it was added lead tetraacetate cake, the diacetone alcohol being in slight stoichiometric excess. The system was heated to about 85 C., whereupon vigorous reaction took place. Water washing of the reaction product removed one of the products, acetone. The other product, insoluble in water, was acetoxyacetol, and this product wasdried over anhydrous sodium sulfate. This product was obtained in good yield. 7

Example 4.- -Oxia'ation of heptaldol The reaction of heptaldol with lead tetraacctatein slight stoichiometric excess in benzene solution was carried out at 35-45 C. The reaction was completed in hours, the reaction mixture being vigorously stirred during this period. The products of the cleavage reaction, heptaldehyde and alpha-acetoxy-heptaldehyde, were isolated and recovered in good yields.

Example 5.-0xidation of methyl ricinoleate Approximately 5500 parts by weight of lead tetraacetate, in the form of the moist cake, together with 2030 parts by weight of methyl ricinoleate and 2265 parts by weight of glacial acetic acid, were placed in a glass flask which was partially submerged in a cooling bath. The flask contents were vigorously mixed for 15 hours, the temperature thereof not being allowed to go higher than 40 C. The unreacted lead tetraacetate was then separated by filtration. The resulting filtrate was mixed with 4000 parts by weight of Water to cause a phase separation. The top phase was separated, washed free of acetic acid and lead acetate. and the washings were discarded.

The sodium citrate was used in slight (543 parts by weight) was added in increments.

The washed phase was then subjected to steam distillation. The heptaldehyde layer was separated from the condensate, and was dried over anhydrous sodium sulfate; the yield of the crude heptaldehyde was 420 parts by weight. The top layer of the. distillation residue was separated and dried over sodium sulfate; this product, principally methyl 11-acetoxy-9-undecenoate, was obtained in a yield of 1745 parts by weight.

The heptaldehyde was identified by redistillation, and preparation of the oxime from a portion of the purified material; the melting point of the oxime corresponded to that for the oxime of heptaldehyde, and was unchanged when the experimental oxime was mixed with known heptaldoxime. The indicated methyl ester product, on vacuum distillation, was found to have a boiling point of 80-83 C. at 0.5 mm. and a saponification value of 421.7 (theoretical value: 438). Saponification of the methyl ester, followed by acidification, yielded 11-hydroxy-9- undecenoic acid, which was found to have the following analytical constants:

Found Calculated Hydroxyl value 266. 0 280. 5 Hydrogen iodine value" 122.0 126.0 Saponiflcation value 263. 5 280. 5

Azelaic acid was obtained from the methyl ester of acetoxy undecenoic acid by oxidation with potassium permangamate. This showed that the double bond in the undecenoic acid ester was in the 9-10 position.

Example 6.-Oxidati0n of methyl ricinoleate Methyl ricinoleate (220 parts by weight) and glacial acetic acid (1070 parts by weight) were placed in a glass flask which was partially submerged in a cooling bath. The flask contents were vigorously mixed, and red lead The addition of the red lead produced an exothermic effect. The temperature of the flask contents was held at 35 -40 C. for about 1.5 hours, the mixing being continued during this period. It was determined, by means of a negative starch-iodide test, that all of the lead tetraacetate (which had been formed in situ) had reacted by the end of the indicated period.

Tap water was then introduced into the reaction flask to effect a phase separation. After being allowed to settle for 1 hour, the lower phase was siphoned off. The upper phase was steam distilled. The heptaldehyde layer was separated from the condensate, and was dried over anhydrous sodium sulfate. The yield of crude heptaldehyde was 206 parts by weight.

The top layer of the distillation residue was separated, filtered after the addition of a filter aid (Hy F10), and dried over anhydrous sodium sulfate. The product, principally methyl 1l-acetoxy-9-undecenoate, was obtained in a yield of 803 parts by weight. In addition to the properties for this ester shown under Example 5, the product of the instant example had an iodine value of 89.9 (theoretical value: 98.8).

Example 7.-Oxidati0n of methyl ricz'noleate Example 5 was repeated, using .caproic acid as the reaction medium and lead tetracaproate as the cleavage reagent The reaction temperature was maintained at about C. 1 The heptaldehydeformed in this reaction was recovered as indicated in Example 5; the other prod uct, methyl- 1l-capro-oxy-9-undecenoate, was also recovered in good yields, the recovered product having a saponification value of 357.2 (theoretical .value: 368.5).

Example 8.'Oxidation of ricinoleyl alcohol the product yielded 81 parts by weight of heptaldehyde. The residual acetoxy product was fractionated under reduced pressure to recover ll-acetoxy 9-undecen-l-ol, which boiled at 133-37 C. at a pressure of 1.0-1.2 mm. The refractive index at 25 C. of this product was 1.4586, and its hydroxyl value was 244.4 (theoretical value: 246). S'aponification of this product yielded 1,11'dihydroxy-9- undecene; the latter product had an iodine value of 127.6 (theoretical value: 136.5).

Example 9.--xidation of castor oil 2030 parts by weight of No. 1 castor oil were reacted With a slight stoichiometric excess of lead tetraacetate cake in 2265 parts by weight of glacial acetic acid, according to the method used in Example 5. The heptaldehyde was separated from the washed product by carbon dioxide sparging. The acetoxy product, glyceryl tri-(llacetoxy-9-undecenoate), was obtained in good yield (1796 parts by weight) and had an iodine value of 90.2 (theoretical value: 99.5).

Example 10.-Oxidation of butyl ester of castor oil fatty acids 2380 parts by weight of the butyl ester of castor oil fatty acids were reacted with a slight stoichiometric excess of lead tetraacetate according to the method of Example 5. The heptaldehyde was removed from the washed product by carbon dioxide sparging. The acetoxy product, butyl 11-acetoxy-9-undecenoate, was vacuum distilled; the iodine value of the purified material was 83.0 (theoretical value: 82.2).

Example 11.0xidati0n of castor oil fatty acids Example was repeated, substituting castor oil fatty acids for the methyl ricinoleate. The residue from the steam distillation, containing principally l1-acetoxy-9- undecenoic acid, was found to boil at 75-85 C. at 1.5-2.0 mm, and to have :an acid value of 218.2 (theoretical value: 231.5).

Example I 2.Oxidation of m thyl ricinoleate Example 5 was repeated, using dichloroethylene as the reaction medium instead of glacial acetic acid. The reaction :and product were substantially identical to those reported under Example 5.

Numerous modifications and variations in the invention described herein will be apparent to those skilled in the art, and are within the spirit and scope of the appended claims.

What is claimed is:

1. A process for the cleavage of aliphatic compounds characterized by the formula:

R -G(OH)-CHC=R I R R wherein R is selected from the group consisting of H, COOH, and alkyl groups, R is selected from the group consisting of H and alkyl groups, R is selected from the group consisting of H, alkyl, OH, and OM groups, wherein M is an alkali metal, R is selected from the group consisting of H and monovalent aliphatic groups, the latter being made up of atoms selected from the group consisting of C, H, and O atoms, and R is selected from the group consisting of O and di-valent aliphatic groups, the latter being made up of atoms selected from the group consisting of C, H, and O atoms, together with, when R contains a COOH group, the salts and amides thereof, said cleavage taking place at the bond joining the carbon atoms to which the R and R groups are attached and resulting in the formation of a -o=o l and acyloxy CHC==R in h which comprises mixing a tetravalent lead compound, selected from the group consisting of lead salts of alkyl carboxylic acids having from 2 to 6 carbon atoms per molecule and lead compounds which yield said salts on reaction with said acids, with a solution of said aliphatic compound undergoing cleavage in a suitable solvent, and agitating the resultant reaction mixture.

2. The process of claim 1, in which said tetravalent lead compound is a salt of an alkyl carboxylic acid having from 2 to 6 carbon atoms per molecule.

3. The process of claim 1, in which said tetravalent lead compound is one which yields salts of alkyl carboxylic acids having from 2 to 6 carbon atoms per molecule on in situ reaction with said acids.

4. The process of claim 1, in which said tetravalent lead compound is used in slight stoichiometric excess.

5. The process of claim 1, in which said tetravalent lead compound is lead tetraacetate.

6. The process of claim 1, in which said solvent is an alkyl carboxylic acid having from 2 to 6 carbon atoms per molecule.

7. The process of claim 1, in which said cleavage is eifected at a temperature of from about 10 to about 200 C.

8. The process of claim 1, in which said cleavage is effected at a temperature in the range from about 35 C. to about 45 C., the reaction being continued until cool- .ing of the reaction mixture is not required to maintain the temperature thereof in said range.

9. The process of claim 1, in which said aliphatic compound subjected to the cleavage reaction is characterized by having R and R representing alkyl groups and R representing hydrogen.

10. The process of claim 1, in which said aliphatic compound subjected to the cleavage reaction is diacetone alcohol.

11. 'Ihe process of claim 1, in which said aliphatic compound subjected to the cleavage reaction is characterized by having R representing a carboxyl group, R representing hydrogen, and R representing a hydroxyl group.

12. The process of claim 1, in which said aliphatic compound subjected to the cleavage reaction is selected from the group consisting of citric acid and the alkali metal salts of citric acid.

13. The process of claim 1, in which said aliphatic compound subjected to the cleavage reaction is characterized by having R and R representing hydrogen and R representing an alkyl group.

14. The process of claim 1, in which said aliphatic compound subjected to the cleavage reaction is heptaldol, a compound in which R and R represents hydrogen, R represents a C5H11 group, R represents a C6H13 group, and R represents oxygen.

References Cited in the file of this patent Vargha: Nature, 162 (1948), 927-8. Johnson et al.: Science Progress, 39 (1951), 96-103. 

1. A PROCESS FOR THE CLEVAGE OF ALIPHATIC COMPOUNDS CHARACTERIZED BY THE FORMULA: 